Joshua trees in Joshua Tree National Forest. Photo by pinoyphotographer on Flickr (noncommercial use permitted with attribution / no derivative works).
Grapevine Mesa Joshua Trees
The Grapevine Mesa Joshua Trees forest (located in Mohave County, AZ) was designated a National Natural Landmark in 1967.
3,206 acres owned by the Federal government, the forest contains the best existing display of Joshua trees in the United States. This site is also a superb example Mojave Desert ecology.